Hydrocleaning machines use high pressure water jets for numerous cleaning purposes. Such hydrocleaning machines, commonly referred to as pressure washers, typically comprise a motor, generally of the internal combustion type, a pump/piston guide unit having reciprocating pistons driven by an oscillating plate fixed to the motor shaft, and an intermediate flange for connecting the piston guide unit to the motor which includes thrust and/or radial bearings for the motor shaft. Such hydrocleaning machines are relatively expensive to manufacture by virtue of the multiplicity of components and the sealing requirements for high pressure operation. Besides the need for the intermediate flange between the motor and piston guide unit, which markedly increases the size of the conventional pressure washers, special seals are required to avoid lubrication losses.